Question

Could you explain steps 1-6 please?

TABLE C-6: STEPS IN LRFD DESIGN PROCESS FOR BRIDGE SUPPORTED ON SHALLOW FOUNDATIONS Step Responsible Disciplines Structural, in coordination with general civil and environmental considerations and geotechnical for approach stability Geotechnical, in coordination with structural, general and environmental LRFD Design Activity Develop preliminary bridge layout. The desired bridge type, size and location will be established. Span lengths and pier locations will be defined, considering geometrical and environmental constraints. Determine the shallow foundation feasibility based on review of existing geologic and subsurface data. Competent bearing material must be present within a reasonable distance from the ground surface. A preliminary assessment of approach embankment stability should be conducted to evaluate potential impacts to abutment locations and span lengths. (Section 4.1). A site reconnaissance with the structural and general civil engineer should be completed at this stage to evaluate constructability of foundation types (Section 4.2). Determine the depth of the footing so that it will not be susceptible to scour potential or frost (Section 6.2). Determine the loads applied to the footing (Section 6.3). Determine the design soil properties from the subsurface exploration and laboratory testing program (Sections 4.3 and Geotechnical, in coordination with structural, general and environmental Hydraulic, with geologic input from geotechnical Structural Geotechnical

Answer 1

Step 1) For Construction of a bridge Structural Engineer will decide the type of bridge based on the traffic data and the location of the site in consultation with Highway Engineer and Environmental Engineer. Every Major Project in Civil Engineering involve Environmental Impact Assessment which is done by Environmental Engineer who will study the impact of Construction of this bridge on Environment and after it is certified by Environmental Engineer then only construction phase can start. After getting clearance from Environmental Engineer and deciding the type of Bridge, size ( width of bridge, length of bridge and height of bridge) is decided and it's location is finalized. Depending upon the Country where the bridge is being constructed, suitable codes are used and decision by Structural Engineer to decide the span length and pier location in consultation with Geotechnical Engineer and general civil engineer.

Step 2) As the bridge is to be constructed on shallow foundation from the past Geotechnical data of that site is studied to study the feasibility of that site and location. As shallow foundation have less depth than suitable material must be there just below the ground surface to Bear the loads of the bridge and the vehicles that will move on it. This will be carried out by Geotechnical Engineer and co-ordinate it with Structural Engineer. As bridge construction also involve abutments construction Geotechnical Engineer co-ordinate the data with General Civil Engineer.

Step 3) Structural Engineer and General Civil Engineer should visit the site where the bridge will be constructed with Geotechnical Engineer who will explain the site to them with the existing data about the soil profile so that Structural Engineer and general civil engineer could make their engineering decisions based on it. Structural Engineer then will decide based on site reconnaissance and existing Geotechnical data about the suitability of shallow foundation at each pier or a different type of foundation is required.

Step 4) Footing Depth is then determined based on the geology of the area and water characteristics of that Hydraulic Engineer will study if there any hydraulic Structure nearby or the depth of water below ground level such that it does not interfere with the foundation depth and geology Engineer will study the Geology of that area and frost does not effect on the depth of the footing by making changes in the geotechnical properties of the site.

Step 5) Based on the Traffic data and factor of safety with suitable margins Structural Engineer will estimate the load of overall bridge and the moving loads of the traffic, wind load on bridge, seismic load on bridge by computer means or by manual means. Usually Computer Softwares are used to estimate the overall load of the bridge and the moving loads of the vehicle. As all the loads of the super Structure must transfer to the foundation , loads on each footing is calculated. For the loads on footing reactions of the node points are calculated in softwares and noted. This work is done only by Structural Engineer.

Step 6) After knowing the loads on the foundation and depth of foundation Structural Engineer needs to find out the size of the foundation that will bear the loads and transfer to the soil. For this we could not rely on the past Geotechnical data as Structure like bridge is very important Structure and must be carefully designed. So Geotechnical tests are performed on the site to determine the actual soil sub surface profile and the Soil Bearing Capacity . This will be determined by the Geotechnical Engineer which will perform certain tests on actual soil surface such as Plate load test, Standard Penetration test to know about type , nature and soil bearing capacity. Based on the results of Geotechnical data, Structural Engineer then will decide the size of the Foundation of Bridge. Geotechnical Engineer will collect samples from the site and then will tests those samples in laboratory to get the accurate results of the soil profile and soil bearing Capacity.